1. Field of the Invention
The present invention relates to gas separation membranes made from a polyimide incorporating repeating units, derived from 9,9 disubstituted xanthene dianhydrides and aromatic diamines.
2. Prior Art
U.S. Pat. Nos. 5,101,004; 5,051,520 and 5,097,000 disclose certain 9,9-disubstituted xanthene dianhydrides and methods for preparation. These patents also disclose that the dianhydrides are useful for making polyimides which have advantageous properties. The patents do not, however, disclose a polyimide gas separation membrane based on such dianhydrides.